Dear Bert,
a solution is the 'package'
censre3 by Hughes JP
Reference: Hughes JP: Mixed effects models with censored data with
application to HIV RNA levels. Biometrics, 55:625-629, 1999.
Giovanni
Don MacQueen ha scritto:
I assume you've looked at the NADA package(?) While I don't believe it
goes as far as dealing the mixed effects models, it might give you a
starting point, and possibly some additional references.
-Don
At 9:08 AM -0700 5/12/08, Bert Gunter wrote:
Dear R Fellow-Travellers:
What is your recommended way of dealing with a left-censored response
(non-detects) in (linear Gaussian) mixed effects models?
Specifics: Response is a numeric positive measurement (of volume,
actually);
but when it falls below some unknown and slightly random value
(depending on
how the sample is prepared and measured), it cannot be measured and is
recorded as 0.
There is some statistical literature on this, but I was unable to find
anything that appeared to me to implement a strategy in any R
package. If it
matters, I am less interested in inference than in removing possible
bias in
estimation.
Feel free to respond off-list if you feel that this would not be of
general
interest.
Cheers,
Bert Gunter
Genentech
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dr. Giovanni Parrinello
Department of Biotecnologies
Medical Statistics Unit
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